1. Field of the Invention
The present invention relates to an ink jet printing apparatus which forms an image by applying to a print medium a coloring material that coagulates under a predetermined condition. More specifically, the present invention relates to an ink jet printing method and printing apparatus that realizes a “marginless printing” by which a print medium is printed with an image without blank edges.
2. Description of the Related Art
As office equipment such as computers, word processors and copying machines advance, a growing number of printing apparatuses for outputting information from these equipment has become available on the market. The printing apparatus employing an ink jet printing system in particular has an advantage of being able to reduce the size of a print head easily, print an image at high resolution and high speed and print on plain paper without requiring special processing on the paper. Other advantages include low running cost, low noise and a relative ease with which a full color printing can be realized using multiple color inks. It has therefore found a wide range of applications, including personal users.
Such a widespread use can lead to the user making new demands on the ink jet printing apparatus. In recent years in particular, there are growing calls for increased image fastness such as waterfastness and lightfastness while maintaining a high color saturation. One method of enhancing the image fastness is to make some improvements on the print medium as dedicated paper. However, to stably maintain a high image fastness of various kinds of print mediums including plain paper, it is more effective to provide an ink itself with some features to achieve the above objective. For this reason, recent years have seen many novel inks developed and their applications proposed.
For example, Japanese Patent Application Laid-open No. 11-227229 (1999) discloses, in addition to the conventionally used dye inks, the development of inks containing pigments as coloants materials and a variety of printing methods using such inks. The inks containing pigments tend to stay on the surface of a print medium with the colorants in a coagulated state, when compared with inks containing dyes as colorants. Thus, the pigment colorants have features of a high color saturation which is not easily faded by sunlight and ozone. To take advantage of both the superiority of the pigment ink and the superiority of the dye ink, the above-cited reference discloses a method that selectively uses these different kinds of inks according to the kind of print medium used and the kind of image to be output. For example, the above document describes that a pigment-based black ink with low penetrability and dye-based color inks with high penetrability are prepared and that a black image may be printed with the black ink or with a combination of different color inks, depending on the kind of print medium and the kind of image to be printed. The cited reference also describes printing color inks first, followed by a black ink overlapping the first printed color inks.
Other methods for enhancing the color saturation and the image fastness propose using a reaction liquid that reacts with color inks containing colorants to make the colorants insoluble or coagulate. For example, Japanese Patent Application Laid-open No. 56-89595 (1981) discloses a method which applies a polymer solution, such as carboxymethyl cellulose, polyvinyl alcohol and polyvinyl acetate, to the print medium before printing and then prints coloring inks. Japanese Patent Application Laid-open No. 63-29971 (1988) discloses a method that involves applying to a print medium a liquid containing an organic compound having two or more cationic groups in one molecule and then printing coloring inks containing anionic dye. Japanese Patent Application Laid-open No. 64-9279 (1989) discloses a method that first applies an acidic liquid containing succinic acid to a print medium and then prints coloring inks. Japanese Patent Disclosure No. 64-63185 describes a method that applies to a print medium a liquid that makes a dye insoluble, before printing coloring inks containing the dye. Japanese Patent Application Laid-open No. 5-202328 (1993) describes a method which applies a reaction liquid containing polyvalent metal ion before printing coloring inks.
Further, Japanese Patent Application Laid-open Nos. 6-106841 (1994), 9-11850 (1997), 11-334101 (1999) and 11-343441 (1999), and U.S. Pat. Nos. 5,428,383, 5,488,402 and 5,976,230 disclose a set of a black ink and coloring inks in which at least one of the color inks exhibits a mutual reactivity with the black ink, with other inks showing no reactivity with the black ink.
All these methods listed above that use a reaction liquid are characterized in that the reaction liquid chemically reacts with the coloring inks containing colorants to coagulate the coloring inks. That is, many ink jet printing apparatus of recent years, whether they use pigments or dyes or whether they require a reaction liquid to induce coagulation, have the colorants coagulate, remain and settle on the surface of a print medium, thereby realizing a satisfactory color saturation and image fastness.
There are also growing calls for a high image quality and a handling that match those of silver salt pictures. In recent years, an increasing number of printing apparatus are appearing on the market which can perform the so-called “marginless printing” by which an image is printed to the edges of the print medium.
In the conventional ink jet printing apparatus, forming an image to the edges of the print medium poses many problems to the apparatus. One of the problems is that ink that has overrun the edges of the print medium may contaminate the interior of the printing apparatus, further contaminating sheets of print medium as they are fed into the printing apparatus. Since the ink is absorbed also at the edges of the print medium, the accuracy with which the print medium is transported degrades, which is likely to result in the print medium being jammed in the apparatus.
However, a construction and method to solve the above problems accompanying the “marginless printing” have already been proposed, for example, in Japanese Patent Application Laid-open Nos. 10-128964 (1998) and 2000-351205. As a construction to realize the “marginless printing” on side edges of a print medium, Japanese Patent Application Laid-open No. 10-128964 (1998) discloses an “ink jet printing apparatus which comprises: a guide means set movable, according to the size of the print medium, in a direction perpendicular to the direction of transport of the print medium and installed inside of the side edges of the print medium; and an ink receiving means installed outside of and adjacent to the guide means in a direction perpendicular to the print medium transport direction to receive ink from the print head.” That is, when the “marginless printing” is performed on print mediums of various widths, ink ejected outside of the side edges of the print medium can be received by the ink receiving means, thereby minimizing the contamination of the interior of the printing apparatus.
Japanese Patent Application Laid-open No. 2000-351205 discloses a construction to realize the “marginless printing” with respect to front and rear ends of a print medium. In this construction, a platen surface that restricts the position of the print medium during printing is formed with a hole and ink ejected outside the front or rear ends of the print medium during the printing operation is led into the hole, in which an absorbent is installed to absorb wasted ink. The mechanism to collect ink ejected outside the edges of the print medium without contaminating the interior of the apparatus is one of the important factors in realizing the “marginless printing.”
In the ink jet printing apparatus, however, it is found that executing the “marginless printing” by using the above-described ink that accelerates coagulation of colorants can cause another problem. This is explained in the following.
When a coagulating ink is used, a quick absorption of ink as with common dye inks becomes difficult to achieve. Such an ink has colorants not dissolved in water and ionized as with dyes but dispersed in a liquid, so when it adheres to the absorbent, it is not absorbed as quickly as water. The phenomenon and problems that the inventors of this invention have found in the process of executing the “marginless printing” using pigment inks as an example of coagulating inks and also dye inks will be explained as follows.
FIG. 13 shows a dye ink as it is ejected onto an ink absorber. In the figure, denoted by 1 is a print head. Ink ejected from the print head 1 is a conventionally known water-based dye ink for use in ink jet printing. The dye used may include water-soluble dyes such as a direct dye, an acid dye and a basic dye. Denoted by 2 is an ink absorber which may use any type of commonly known porous material. The ink absorber may be formed, for example, by using fibers of cellulose, rayon, acrylic, polyurethane or polyester singly or in combination and forming these fibers into fibrils or by subjecting the fibers to a hydrophilic treatment and laminating them in layers. The ink absorber may also be formed of porous polyethylene and melamine foam. If such an ink absorber 2 is used in combination with the dye ink, the ink will quickly be absorbed in the ink absorber, with the ink soaking into the interior of the ink absorber 2 as shown shaded in the figure.
FIG. 14 shows a pigment ink as it is ejected onto an ink absorber similar to the above. Any conventionally known pigment ink for use in ink jet printing may be used. In a combination of such a pigment ink and the ink absorber, a part of ink components such as liquid medium penetrates into the ink absorber 2. However, the pigment particles remain on the ink absorber 2 forming a deposit as an ink component left unabsorbed. That is, as shown shaded in the figure, the ink separates into a portion that penetrates into the absorber and a portion that deposits on the ink absorber and settles there.
While in the above explanation a pigment ink has been taken for example, such an ink behavior in the absorber can similarly be observed in any ink with a coagulating colorant. For example, the same also applies even to an ink composed of a mixture of dye and pigment in which the pigment constitutes a main colorant with another colorant such as a highly soluble dye mixed with it for color adjustment. The similar effect can also be produced even when a dye is used as a colorant, by using a reaction liquid that reacts with the dye to accelerate the coagulation of the colorant.
In the absorber during the execution of the “marginless printing”, the ink deposit on the surface of the absorber progressively increases as the number of printed sheets and the power-on time increase. Once the surface of the absorber is covered with the deposit, ink droplets landing on the absorber thereafter fail to be received in the absorber. As a result, ink bounced off the absorber surface will contaminate the interior of the printing apparatus. Further, when a large number of sheets are “marginless-printed”, it is found that the ink deposit reaches the print medium transport path, contaminating the back of the print medium. Furthermore, it is also found that the ink deposit may protrude even into the print medium transport path, touching the end of the print medium, which in turn may result in a transport failure.
Because of various problems described above, a satisfactory “marginless printing” is difficult to achieve in the ink jet printing apparatus that uses inks with a coagulating property.